Relative positioning system and method

ABSTRACT

A relative positioning system and method has an adjoining pair of spaced apart receivers positioned proximal to an object causing a signal interference with a radio frequency signal detectable by each receiver of the adjoining pair. The radio frequency signal is associated with an emitter. Control electronics operatively couple the spaced apart receivers. The control electronics are configured to determine a direction of the emitter based on the signal interference. In an embodiment of the system and method the emitter is associated with an object of interest, the signal encodes information relating to the identity and status of the object, and information and heading of the object are cutaneously communicated to an operator by an article worn by the operator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of PCT/US2007/020486 filedSep. 21, 2007, entitled “Relative Positioning System And Method” andclaims the benefit of priority of related to U.S. Provisional PatentApplication No. 60/846,407, entitled “Wearable Multi-sensory MedicalDisplay”, filed Sep. 21, 2006, U.S. Provisional application No.60/846,827, entitled “Advanced Dynamic Relative Positioning”, filed Sep.21, 2006, U.S. Provisional application No. 60/974,003 entitled “WearableRelative Positioning System and Method”, filed Sep. 20, 2007. Each ofthe above-identified related applications is incorporated herein byreference.

STATEMENT REGARDING FEDERALLY RESEARCH OR DEVELOPMENT

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms to the extent and under the provisions asprovided for by the terms of Contract No. DAH001-05-S-0144 awarded bythe U.S. Air Force Special Operations Command (AFSOC).

BACKGROUND OF THE INVENTION

Dynamic environments, and in particular emergency or catastrophicenvironments, subject those present to extreme and hostile conditions inwhich to accomplish specific missions or task requiring the location andthe assessment of the status of objects of interest. One example of arepresentative mission requiring real time, dynamic relative positioningis that of an emergency medical technician or other emergency careprovider. An alternative, but no less equally important mission,includes the need for members of a relief team responding to a naturaldisaster (e.g., a hurricane or earthquake) to maintain situationawareness of the environment at all times and in all conditions (e.g.,poor visibility), and in particular to locate, treat, and monitorcasualties and where appropriate to locate, track and monitor other teammember activities.

To achieve mission success during catastrophes or other extremely highworkload conditions, a emergency medical technician or other emergencycare provider must receive large amounts of casualty medicalinformation, and is required to maintain situation awareness of thebattlefield environment at all times and in all conditions. All priorsolutions have used two dimensional visual displays (for example,Personal Digital Assistants or laptops) to display the casualty medicalinformation. These current visual displays demand the operator's visualattention that can compromise mission effectiveness, and operations inlow light visibility environments can cause fatigue, degradeperformance, and compromise clandestine operations. The operator couldbe much more effective and efficient if his eyes were used to survey hissurroundings rather than continuously monitoring a visual display.

Accordingly, there is a need in the art for a device that enhances theability of the emergency medical technician or other operator to locate,assess, track and monitor objects of interest (including but not limitedto casualties) in a dynamic environment.

SUMMARY OF THE INVENTION

Briefly stated, one aspect of the present invention is a relativepositioning system comprising: an article wearable by an operator; atleast two radio signal receivers positioned on the article spaced apartaround the operator wearing the article such that the operator causessignal interference with a radio frequency signal detectable by eachreceiver, the radio frequency signal being associated with an emitter;control electronics on the article operatively coupling the spaced apartreceivers and configured to determine a direction of the emitterrelative to the operator based on the signal interference relative tothe human body; and a plurality of stimulus generators supported by thearticle operatively connected to the control electronics and to theoperator wearing the article, each stimulus generator able to generate astimulus perceptible to the operator wearing the article; wherein thecontrol electronics activates one of the plurality of stimulusgenerators so as to provide a direction cue to the operator as to thedirection of the emitter relative to the operator.

Another aspect of the present invention is a method for achievingoperator awareness of a casualty in an emergent environment, thecasualty having a heading with respect to the operator and emitting asignal having a strength. The method comprises the steps of: positioningon the operator a wearable article supporting a two-dimensional,body-centered coordinate system formed by a plurality of receivers and aplurality of stimulus generators, each receiver of the plurality ofreceivers able to receive the signal from the casualty, each signalgenerator of the plurality of stimulus generators able to generate astimulus perceptible to the operator, the plurality of receiversoperatively coupled to the plurality of stimulus generators by controlelectronics; detecting with the plurality of receivers the signalemitted by the casualty; determining the heading of the casualty in thebody-centered coordinate system; and communicating to the operator adirectional cue corresponding to the heading, the directional cuegenerated by one stimulus generator of the plurality of stimulusgenerators.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofpreferred embodiments of the invention, will be better understood whenread in conjunction with the appended drawings. For the purpose ofillustrating the invention, there is shown in the drawings embodimentswhich are presently preferred. It should be understood, however, thatthe invention is not limited to the precise arrangements andinstrumentalities shown.

In the drawings:

FIG. 1 is a schematic diagram of a preferred embodiment of the wearablerelative positioning system in accordance with the present invention;

FIG. 2 is a schematic diagram of the of the embodiment of FIG. 1 showingthe sectors of the two-dimensional, body-centered coordinate system;

FIG. 3 is a digital image of a wearable pod housing a portion of theembodiment of FIG. 1;

FIGS. 4( a), (b) and (c) are graphic representations of the differentialdegradation in the strength of the signal detected by three pairs S1,S2, S3 of the plurality of receivers in accordance with the embodimentof FIG. 2;

FIG. 5 is a schematic diagram of the embodiment of FIG. 2 showing thesectors of the two-dimensional, body-centered coordinate system for anenvironment having a plurality of casualties;

FIG. 6 is an example of a preferred scheme for prioritizing the statusof casualties in accordance with the present invention;

FIGS. 7 a and 7 b are a schematic diagrams (front and side) of apreferred embodiment of a receiver with shielding in accordance with thepresent invention; and

FIG. 8 is a functional flow diagram of the steps of a preferredembodiment of a method for achieving operator awareness of a casualty inan emergent environment in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology is used in the following description for convenienceonly and is not limiting. For example, the words “right,” “left,” and“front” designate directions in the drawings to which reference is made.The terminology includes the words noted above, derivatives thereof andwords of similar import.

Broadly stated, the present invention relates to a system and method fordetermining the position of one or more objects of interest in dynamicenvironments. More specifically, the present invention includes awearable relative positioning system for determining relative to thebody of an operator a wearing the system heading of the objects ofinterest in the dynamic environments and for maintaining an awareness ofthe status of the objects of interest.

One aspect of the invention is a relative positioning system comprisingan adjoining pair of spaced apart receivers 16 positioned proximal to anobject causing a signal interference with a radio frequency signal 12detectable by each receiver of the adjoining pair. The radio frequencysignal 12 is associated with an emitter 22 attached to a distal objectof interest. Control electronics 20 operatively couples the spaced apartreceivers 16. The control electronics 20 is configured to determine adirection of the emitter 22 based on the signal interference.

Referring to the drawings in detail, where like numerals indicate likeelements throughout, there is indicated a relative positioning system iswearable by an operator. In the figures and disclosure to follow, thewearable, relative positioning system is generally designated 10 andhereinafter referred to as the RPS 10 in accordance with the presentinvention. The RPS 10 determines relative to a body of an operator orobject wearing or supporting the RPS 10, a heading of an object emittinga signal 12 having a signal strength. The RPS 10 is not limited to beingworn by a person. The body on which the RPS 10 may be mounted orattached includes animate and inanimate objects such as search dogs,robots, and autonomous unmanned vehicles.

For brevity, the RPS 10 is described below using an example ofascertaining the location and status of scattered, multiple casualties,for example, from a major accident or other catastrophe, and whennecessary, to treat the most critical casualties on a priority basis.Accordingly, in the context of the example, the operator is a emergencymedical technician or physician or the like and the object of interestis a casualty. However, the invention is not limited to such a missionnor is it limited to a casualty situation. For example, as stated above,broadly viewed, the present invention relates to a system and method forlocating and maintaining the awareness of one or more objects ofinterest in dynamic environments.

The RPS 10 preferably comprises an article 14 wearable on the body ofthe operator. The article 14 may be mounted on any wearable structure,such as a belt, a vest, or even a cap, a glove or other garment thatenables cutaneous communication to the operator. Preferably, the RPS 10is configured as a casualty tracker system ensemble (CSTE) belt orsimply “casualty belt” to be worn about an operator's waist.

The RPS 10 comprises a plurality of receivers 16 and a plurality ofstimulus generators 18 operatively coupled by control electronics 20.Each receiver of the plurality of receivers 16 and each stimulusgenerator of the plurality of stimulus generators 18 is preferablysupported by the wearable article 14. Each receiver 16 is able toreceive the signal 12 from the object. Preferably the signal 12 is aradio frequency (RF) signal and at least three RF receivers 16 a, 16 b,16 c are provided. The receivers 16 may be any of a wide variety ofconventional radio frequency (RF) receivers adapted to the desired formfactor and configured to receive an RF signal. Preferably, the RF signalemanates from an electronic tag (also “Etag” or “E-Tag”) 22 attached tothe object of interest, which for the major accident example could be acasualty. The electronic tag 22 may be any of a wide variety of emittersable to transmit an RF signal receivable and decodable by the receivers16 and their associated control electronics 20. At least one receiver ofthe plurality of receivers 16 may be configured to interrogate theelectronic tag 22 and in response to the interrogation, the signal 12emitted from the electronic tag 22. The electronic tags 22 may also beoperatively coupled to status sensors (not shown) on the object which inthe case of a casualty may provide the status of vital signs. Typicallythe RF signal encodes and communicates information representing theidentification and status of the object in a form the controlelectronics 20 can process.

The stimulus generators 18 may be any of a wide variety of stimulusgenerators, each able to generate a stimulus perceptible to theoperator. Desirably the stimulus generators are tractors, and preferablyare any of a wide variety of vibro-tactile stimulators adapted to thedesired form factor and configured to provide cutaneous communication tothe operator. Alternatively, the stimulus generators may be replaced byother perceptible stimulus generator able to communicate two-dimensionaldirectional cueing.

For example, in certain applications and environments where audible orvisible communications are permissible, the cutaneous communication maybe replaced or augmented by audible or visible signals. In suchapplications and environments, the control electronics 20 of the RPS 10may provide audible communication by being operatively coupled to anaudible signal generator or may provide visual communication by beingoperatively coupled to an LCD display able to provide a visible headingindicator and also to provide detail regarding a casualty's vital signs,such as heart rate or medical status (e.g., guarded, stable, critical,etc.) or both. Referring to FIG. 3, in a preferred embodiment, the RPS10 includes an enclosure 24 or pod housing the control electronics 20.The pod 24 may be removably attachable to a belt 14 (partially depictedin phantom) or to the operator's wrist to enable the operator to easilyaccess the operator interface integrated into the pod.

Referring to FIG. 2, a two-dimensional, body-centered coordinate systemindicated generally at 26 is formed by the plurality of receivers 16.Preferably, the plurality of receivers 16 and a plurality of stimulusgenerators 18 are arranged such that they are uniformly spaced with aseparate stimulus generator of the plurality of stimulus generators 18positioned between each adjoining pair of receivers of the plurality ofreceivers 16. The two-dimensional, body-centered coordinate system 26comprises a plurality of sectors 28. Each sector 28 a, 28 b, 28 c,respectively is defined by an adjoining pair S1, S2, S3 of spaced apartreceivers 16 a, 16 b, 16 c of the plurality of receivers 16. A separatestimulus generator 18 a, 18 b, 18 c of the plurality of stimulusgenerators 18 is positioned in each sector 28 a, 28 b, 28 c,respectively.

The control electronics 20 is configured to cause one stimulus generatorof the plurality of stimulus generators 18 to communicate to theoperator a directional cue corresponding to the heading of the objectwith the emitter 22. In a preferred embodiment, the directional cue isdetermined by a trigger algorithm based on a differential degradation inthe strength of the signal detected by the plurality of receivers 16 asfurther discussed below. The differential degradation is caused by theinteraction of the signal with the body of the operator. As shown inFIG. 8, the differential degradation of the signal may be enhanced byshielding 30 located between the body of the operator and at least oneof the receivers of the plurality of receivers 16.

The control electronics 20 causes the one of the stimulus generators 18to communicate the directional cue to the operator by executing atrigger algorithm based on a sum of the strength of the signal receivedby each of the receivers 16 of each adjoining pair of spaced apartreceivers defining the sector in which the signal emanates.

The receivers and signal generators may be operatively coupled (eitherby wire, fiber or wirelessly) to control electronics 20 housed in a pod,such as the pod shown in FIG. 3. Alternatively, the control electronics20 may comprise a plurality of loosely coupled autonomous agents. Eachagent may be able to communicate with each other agent. At least oneagent may be uniquely associated with one receiver of the plurality ofreceivers 16 or with one stimulus generator of the plurality of signalgenerators 18.

Referring to FIG. 2, in a preferred embodiment, the plurality ofreceivers 16 comprises a first receiver 16 a, a second receiver 16 b anda third receiver 16 c and the plurality of stimulus generators 18comprises a first tractor 18 a, a second tractor 18 b, and a thirdtractor 18 c. The plurality of receivers 16 and the plurality ofstimulus generators 18 are uniformly spaced with a tractor 18 a, 18 b,18 c positioned between each adjoining pair 16 a:16 b, 16 b:16 c, 16c:16 a of receivers. As shown in FIG. 2, the arrangement of theadjoining pairs of receivers provides three sectors or sections (left 28a, right 28 b and front 28 c) for directional cueing. Receivers 16 a and16 b, acting as a pair S1, form signal strength collector (Set 1) forthe left sector 28 a; receivers 16 b and 16 c, acting as a pair S2, forma signal strength collector (Set 2) for the right sector 28 b; andreceivers 16 c and 16 a, acting as a pair S3, form a signal strengthcollector (Set 3) for the front sector 28 c. For each sector, the sum ofthe signals received by the corresponding pair (or Set S) of receiversprovides the basis for determining whether a signal is arriving fromthat sector. Additional receivers and tractors may be provided toincrease the number of sectors, the number depending on the desiredresolution for the directional cueing.

FIG. 2 schematically shows a radio signal source in the form of anelectronic tag 22 in the focus of the front sector 28 c. The bars inFIG. 4 show the combined strength of the signal 12 for each of thereceiver pairs (sets): S1 (16 a:16 b); S2 (16 b:16 c); S3 (16 c:16 a),due to the presence of electronic tag 22. Pair set S3 in this examplereceives the strongest signal. Directional cueing is provided byactuating the stimulus generator (or tractor) 18 c associated with thefront sector 28 c and pair set S3 in response to a trigger algorithmemploying the simple logic for analyzing relative signal strength.

In FIG. 2, the receivers 16 a, 16 b, 16 c and the stimulus generators(or tractors) 18 a, 18 b, 18 c are uniformly spaced from one another.The presence of the emitter 22 in the sector defined by the receiverpair 16 a, 16 c causes the tractor 18 c to fire as the sum R1+R3 of thestrength of the signals received by the set 3 receiver pair 16 a, 16 c(FIG. 4( c)) is greater than the sum R1+R2 of the strength of thesignals received by the set 1 receiver pair 16 a, 16 b (FIG. 4( a)) andalso is greater than the sum R2+R3 of the strength of the signalsreceived by the set 2 receiver pair 16 b, 16 c (FIG. 4( b)). Theactivation (firing) of tractor 18 c provides the directional cue for theheading (or relative position) of electronic tag 22, as the signalstrength of Set 3 is greater than the strength of the signal received byboth Set 1 and Set 2. As stated above the trigger logic may be executedby a central processor or by logic circuits associated with eachreceiver and/or tractor.

Referring to FIGS. 5 and 6, in environments where multiple independentlyidentifiable electronic tags 22 a, 22 b, 22 c, 22 d, each associatedwith a different object, are present in the mission environment, apreferred embodiment of the invention may be configured to providesituation awareness of not only the heading of each of the objects butalso the status. The individual possible status codes for such casualtyare defined in FIG. 6. They can be employed on a visual operator displayusing shape or color codes or both, if provided. FIG. 5 schematicallyrepresents such a situation in the major accident example above.Depicted in FIG. 5 are the electronic tags 22 a, 22 b, 22 c, 22 dassociated with four different casualties (or patients). The casualtycorresponding to electronic tag 22 b is in stable condition(green/circle). The casualties corresponding to electronic tag 22 a andelectronic tag 22 d are not well but also are not in critical condition(yellow/squares). The casualty corresponding to electronic tag 22 c isin critical condition and requires attention (red/triangle).

As the RF signals transmitted by each of the electronic tags preferablyinclude a unique identification number and also casualty statusinformation, this embodiment of the RPS 10 determines in the mannerdiscussed above the directional heading of each casualty. Furthersoftware executed by the control electronics prioritizes the casualtylocation and determines the criticality of the casualty. The softwarethen determines the tactile algorithm and visual indicator to becommunicated to the operator. For example, for a stable casualty, thetactile signal is a low intensity signal and the visual indicator is agreen circle. For an emergent casualty (unwell but not critical) thetactile signal is a medium intensity signal and the visual indicator isa yellow square. For a serious casualty (critical), the tactile signalis a high intensity signal and the visual indicator is a red triangle.Preferably, only the most critical casualty (-ies) is/are displayedusing the tactile display while the entire battlefield casualty statusis displayed a visual display. In summary, if the casualty is in theright rear sector and has a status of critical, the tractor locatedbetween the adjoining receiver pairs defining the sector will activateat a high intensity and a red triangle will appear on the visual displayof the RPS 10. Alternatively, audible cues varying in tone or intensitybased on the severity of the medical status may be communicated to theoperator instead of or in addition to the visual cues.

Further, in accordance with a rule based updating paradigm, such asupdate the status of stable casualties every 120 seconds, unwell but notcritical casualties every 60 seconds, and critical casualties every 10seconds, situational awareness for multiple casualties is achieved byautomatic tactor firings based on the incoming update frequencies.Updates could be generated automatically from the electronic tag, if itis configured to process status information from the casualty or otherobject of interest, from the control electronics 20 based on data fromthe electronic tag(s) processed by the control electronics to ascertainelectronic tag wearer medical status or entered manually by the beltwearer.

The electronic tags 22 may be transponder-like devices that onlytransmit when interrogated and the receivers may be configured tointerrogate the transponders at predetermined or operator selectableintervals.

A more detailed description of another aspect of the invention isdiscussed below in the context of the major accident mission describedabove.

FIG. 8 illustrates a method for achieving operator awareness of acasualty in an emergent environment, generally designated 100, andhereinafter referred to as the casualty tracking method 100. Thecasualty to which the casualty tracking method 100 is directed has aheading with respect to the operator and emits a signal 12 having astrength. Preferably, the signal 12 encodes information representing theidentity of the casualty and the vital signs of the casualty.

The casualty tracking method 100 comprises a positioning step 110 inwhich a wearable article, such as the article 14 described above, ispositioned on the operator. The article supports a two-dimensional,body-centered coordinate system 26 formed by a plurality of receivers 16and a plurality of stimulus generators 18. Each receiver of theplurality of receivers 16 is able to receive the signal 12 from thecasualty. Each signal generator of the plurality of stimulus generators18 is able to generate a stimulus perceptible to the operator. Theplurality of receivers 16 are operatively coupled to the plurality ofstimulus generators 18 by control electronics 20.

The casualty tracking method 100 has a detecting step 120 in which thesignal 12 emitted by the casualty is detected with the plurality ofreceivers 16. In instances where the casualty is one casualty of aplurality of casualties, the detecting step detects the signal emittedby each casualty.

In a determining step 130, the casualty tracking method 100 determinesthe heading of the casualty in the body-centered coordinate system. Asdiscussed above, the heading determination may be based on adifferential degradation in the strength of the signal detected by theplurality of receivers 16. The differential degradation may be caused bythe body of the operator. If the signals emitted by the casualty containinformation related to vital signs, in addition to the heading, thedetermining step 130 also determines the medical status of each casualtybased on the associated vital signs.

A prioritizing step 140 prioritizes the medical status of each casualtybased on the severity of the medical status. An associating step 150associates the directional cue with the casualty having a highestprioritized medical status.

The casualty tracking method 100 has a communicating step 160 in which adirectional cue corresponding to the heading is communicated to theoperator. The directional cue is generated by one stimulus generator ofthe plurality of stimulus generators. The communicating step 160 mayalso communicate to the operator the severity of the medical status asan intensity of the directional cue. As discussed above, in certainapplications and environments where audible or visible communicationsare permissible, the cutaneous communication may be replaced oraugmented by audible or visible signals allowing the heading and medicalstatus of each casualty to be communicated to the operator as visibleindicators on a visual display.

Yet another embodiment of the present invention is a method fordetermining a heading of an object emitting a signal having a signalstrength. The method comprises creating a two-dimensional, body-centeredcoordinate system formed by the plurality of receivers. Each receiver isable to receive the signal from the object. The plurality of receiversare operatively coupled by control electronics. Another step in themethod comprises producing with the control electronics a directionalcue corresponding to the heading of the object based on the strength ofthe signal received by each of the plurality of receivers.

Another aspect of the invention is a method for determining a directionof an emitter attached to an object of interest. The method comprises apositioning step in which an adjoining pair of spaced apart receivers 16is positioned proximal to an object causing a signal interference with aradio frequency signal 12 detectable by each receiver of the adjoiningpair. The radio frequency signal 12 is associated with an emitter 22attached to an object of interest. The spaced apart receivers areoperatively coupled by control electronics 20. In a determining step,the control electronics 20 determines a direction of the emitter 22based on the signal interference.

PCT/US2007/020473 filed Sep. 21, 2007, entitled “Apparatus and Methodfor Non-invasive Thoracic Radio Interrogation”; U.S. Patent applicationNo. 60/846,403 entitled “Method and Apparatus for Non-Invasive BioImpedance Determination”, filed Sep. 21, 2006; U.S. Provisionalapplication No. 60/846,402 entitled “Method for Conditioning RadioSignal Returns from Thoracic Components for Extractions ofCardiopulmonary Data”, filed Sep. 21, 2006; U.S. Provisional applicationNo. 60/973,985, entitled “Apparatus and Method for Non-Invasive ThoracicRadio Interrogation”, filed Sep. 20, 2007; PCT/US2007/020487 filed Sep.21, 2007 entitled “Method for Processing Thoracic Reflected RadioInterrogation Signals”; U.S. Patent Application No. 60/846,404 entitled“Method of Processing Thoracic Reflected Radio Interrogation Signals”,filed Sep. 21, 2006; U.S. Patent Application No. 60/973,988 entitled“Method of Processing Thoracic Reflected Radio Interrogation Signals”,filed Sep. 20, 2007; PCT/US2007/020492 filed Sep. 21, 2007, entitled“Antenna for Thoracic Radio Interrogation”; U.S. Provisional applicationNo. 60/846,408 entitled “Transducer-antenna-probe for Thoracic RadioInterrogation”, filed Sep. 21, 2006, and U.S. Provisional ApplicationNo. 60/910,394, entitled “Antenna for Thoracic Radio Interrogation”,filed Apr. 5, 2007, and U.S. Provisional Application No. 60/973,970,entitled “Antenna for Thoracic Radio Interrogation”, filed Sep. 20,2007, are also all incorporated by reference herein in their entireties.

Those skilled in the art will appreciate that changes could be made tothe embodiments described above without departing from the broadinventive concept thereof. Therefore, the wearable relative positioningsystem and method are not limited to the particular embodimentsdisclosed. Rather, the specification is intended to expressly orinherently cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

1. A relative positioning system comprising: an article wearable by anoperator; at least two radio signal receivers positioned on the articlespaced apart around the operator wearing the article such that theoperator causes signal interference with a radio frequency signaldetectable by each receiver, the radio frequency signal being associatedwith an emitter; control electronics on the article operatively couplingthe spaced apart receivers and configured to determine a direction ofthe emitter relative to the operator based on the signal interferencerelative to the human body; and a plurality of stimulus generatorssupported by the article operatively connected to the controlelectronics and to the operator wearing the article, each stimulusgenerator able to generate a stimulus perceptible to the operatorwearing the article; and at least a third radio signal receiverpositioned on the article spaced apart around the operator from the atleast two receivers wherein the spaced apart receivers define atwo-dimensional, coordinate system centered on the operator wearing thearticle, the coordinate system including a plurality of sectors, eachsector defined by an adjoining pair of spaced apart receivers, aseparate stimulus generator being positioned in each sector; and thecontrol electronics activating one of the plurality of stimulusgenerators so as to provide a direction cue to the operator as to thedirection of the emitter relative to the operator and the controlelectronics causing the one stimulus generator to communicate thedirectional cue to the operator by executing a trigger algorithm basedon a sum of the strength of the signal received by each receiver of theadjoining pair of spaced apart receivers defining the sector in whichthe signal emanates.
 2. The relative positioning system of claim 1,wherein the plurality of stimulus generators are tractors able toprovide cutaneous communication.
 3. The relative positioning system ofclaim 1 wherein one stimulus generator of the plurality of stimulusgenerators comprises an operator interface able to provide audiblecommunication.
 4. The relative positioning system of claim 1 wherein onestimulus generator of the plurality of stimulus generators comprises aninterface able to provide visual communication.
 5. The relativepositioning system of claim 1 wherein the radio frequency signal furtherencodes information representing the identification and status of anobject operatively associated with the emitter, and wherein thedirectional cue has an intensity based on the status information.
 6. Therelative positioning system of claim 5 wherein one stimulus generatorcomprises an operator interface able to visually or audibly communicatethe information.
 7. The relative positioning system of claim 1 whereinthe control electronics comprises a plurality of loosely coupledautonomous agents having local decision making logic, each agent able tocommunicate with each other agent, at least one agent uniquelyassociated with one receiver of the plurality of receivers or onestimulus generator of the plurality of stimulus generators.
 8. Therelative positioning system of claim 1 wherein the control electronicsare mounted in a pod separable from the receivers and the stimulusgenerators, the control electronics wirelessly coupled to the receiversand the stimulus generators.
 9. The relative positioning system of claim1, wherein the receivers and the stimulus generators are uniformlyspaced with a separate stimulus generator positioned between eachadjoining pair of receivers.
 10. The relative positioning system ofclaim 1 wherein the article is a belt.
 11. The relative positioningsystem of claim 1 wherein the emitter is on a casualty having vitalsigns, wherein the radio frequency signal encodes informationrepresenting the vital signs and wherein the control electronics furthercomprises an operator interface including a visible display configuredto provide a visible heading indicator and a visible vital signindicator.
 12. The relative positioning system of claim 11, wherein thecontrol electronics are further configured to determine a medical statusof the casualty and to provide a visible medical status indicator. 13.The relative positioning system of claim 12, wherein the casualty is onecasualty of a plurality of casualties, and the control electronics isconfigured to communicate the heading and medical status of eachcasualty of the plurality of casualties.
 14. A method for achievingoperator awareness of a casualty in an emergent environment, thecasualty having a heading with respect to the operator and emitting asignal having a strength, the method comprising the steps of:positioning on the operator a wearable article supporting atwo-dimensional, body-centered coordinate system formed by a pluralityof receivers and a plurality of stimulus generators, each receiver ofthe plurality of receivers able to receive the signal from the casualty,each signal generator of the plurality of stimulus generators able togenerate a stimulus perceptible to the operator, the plurality ofreceivers operatively coupled to the plurality of stimulus generators bycontrol electronics; detecting with the plurality of receivers thesignal emitted by the casualty; determining the heading of the casualtyin the body-centered coordinate system; and communicating to theoperator a directional cue corresponding to the heading, the directionalcue generated by one stimulus generator of the plurality of stimulusgenerators; wherein the determining step determines the heading based ona differential degradation in the strength of the signal detected by theplurality of receivers, the differential degradation being caused by thebody of the operator.
 15. The method of claim 14 wherein the signalencodes information representing vital signs of the casualty and themethod further comprises determining the medical status of the casualtybased on the information representing the vital signs and thecommunicating step communicates to the operator a severity of themedical status as an intensity of the directional cue.
 16. A method forachieving operator awareness of a casualty in an emergent environment,the casualty having a heading with respect to the operator and emittinga signal having a strength, the method comprising the steps of:positioning on the operator a wearable article supporting atwo-dimensional, body-centered coordinate system formed by a pluralityof receivers and a plurality of stimulus generators, each receiver ofthe plurality of receivers able to receive the signal from the casualty,each signal generator of the plurality of stimulus generators able togenerate a stimulus perceptible to the operator, the plurality ofreceivers operatively coupled to the plurality of stimulus generators bycontrol electronics; detecting with the plurality of receivers thesignal emitted by the casualty; and determining the heading of thecasualty in the body-centered coordinate system; and communicating tothe operator a directional cue corresponding to the heading, thedirectional cue generated by one stimulus generator of the plurality ofstimulus generators; wherein the casualty is one casualty of a pluralityof casualties, each casualty emitting a signal encoding associated vitalsigns, wherein the detecting step detects the signal emitted by eachcasualty; wherein the determining step determines the heading of eachcasualty based on a differential degradation in the strength of theassociated signal and determines the medical status of each casualtybased on the associated vital signs; and wherein the method furthercomprises the steps of: prioritizing the medical status of each casualtybased on the severity of the medical status; associating the directionalcue with the casualty having a highest prioritized medical status andcommunicating to the operator the severity of the medical status as anintensity of the directional cue; and communicating to the operator theheading and medical status of each casualty by visible indicators on avisual display.